A wafer employed for producing various kinds of semiconductor devices can generally be obtained by cutting out a crystalline ingot such as Si or GaAs at specific intervals so as to form plates and mirror polishing their surfaces.
A diamond blade saw or a wire saw for metal cutting has heretofore been employed for cutting a crystalline ingot. Namely, an ingot is cut out with impact caused by pressing a diamond blade rotating at a high speed or a wire vibrating at a high speed thereon.
However, there is a problem in cost effectiveness in the above cutting method because it is impossible to cut out only the part cut into by a diamond blade or a wire since the adjacent area of the cut is deformed or destroyed so that an extra space of a sizable thickness is wasted. More specifically, a thickness of about 500 .mu.m is wasted when a piece of wafer is cut out, which means about 50% of an ingot may be wasted when cutting out a wafer of 500 .mu.m in thickness.
In addition, as such tools are repeatedly used in the cutting processes, the edge may be nicked or seizing may be caused, and then the sharpness may deteriorate, so that a diamond blade, a wire, or the like requires time-consuming work of periodical replacement.
Further, there is another problem in that cutting fluid is charged into portions to be cut for cooling and lubrication, and debris caused in a cutting process may scatter, resulting in deterioration of the work environment. Still further, it is difficult to recycle or dispose of the cutting fluid including the debris because a troublesome process, i.e., separation of the debris and the cutting fluid, is required.
Accordingly, it is an object of the present invention to provide a superior method and apparatus for producing a wafer hygienically and easily whereby waste can be minimized in the cutting process.
To accomplish the above objects, a first embodiment of the present invention provides a method for producing a wafer from a crystalline ingot comprising: supplying an etching gas which shows a high etching property for at least one constituent of the crystalline ingot, in a state of a molecular beam stream on a predetermined part of the crystalline ingot to be processed, volatilizing the predetermined part gradually from the surface of the ingot, and finally removing the predetermined part entirely to cut the wafer from the ingot.
A second embodiment of the present invention provides a method according to the first embodiment, wherein the etching gas comprises at least one component which is selected from the group consisting of ClF.sub.3, NF.sub.3, CCl.sub.2 F.sub.2, CF.sub.4, C.sub.2 F.sub.6, C.sub.3 F.sub.8, CHF.sub.3, CCl.sub.4, SF.sub.6, CCl.sub.3 F and HCl.
A third embodiment of the present invention provides a method according to the first or second embodiments, wherein the etching gas is supplied on the predetermined part of the crystalline ingot under a low pressure in the range of 1 to 10.sup.-6 Torr.
The present invention also provides an apparatus for producing a wafer from a crystalline ingot comprising a closed chamber provided with a supporting member for mounting the crystalline ingot and means for holding the wafer cut from the crystalline ingot, means for evacuating the chamber, and means for supplying an etching gas which shows a high etching property for a constituent of the crystalline ingot, in a state of a molecular beam stream on a predetermined part of the crystalline ingot to be processed, which is mounted on the member for mounting the crystalline ingot.
In another embodiment of the apparatus of the present invention, wherein the crystalline ingot to be cut is prismatic, an injector having plural slits formed in parallel is provided to a side of the prismatic ingot, and the etching gas is injected from each of the slits simultaneously so as to cut simultaneously plural wafers.
In the method of the invention, at least one constituent (for example, silicon atoms) of a crystalline ingot enters into a chemical reaction as a result of repeated collisions with atoms or molecules of etching gas, and consequently separates from the ingot surface. "An etching gas exhibiting a high etching property" herein means an etching gas exhibiting a property such that the number of required collisions of the atoms or molecules of etching gas with the constituent of the crystalline ingot to separate the constituent of the crystalline ingot is relatively small, specifically within 10 times. On the other hand, a conventional etching gas (BCl.sub.3, SiCl.sub.4, Br.sub.2 or the like) requires several tens to 100 collisions to cause the separation. Thus there is a great difference in property between an etching gas showing a high etching property and a conventional etching gas.